1. Field of the Invention
The present invention relates to a sealing device for laterally sealing at least one overpressure and vacuum zone adjacent to a moving surface in a paper machine and a process for sealing the moving surface with the sealing device. The sealing device includes at least one sealing element positioned adjacent to the moving surface, a holder in which the sealing element is mounted movably toward and away from the moving surface, and at least one loading element adapted to load the sealing element in the direction toward the moving surface.
2. Discussion of Background Information
Sealing devices such as those generally discussed above have been utilized in forming sections, press sections, and/or dry ends of a paper machine, e.g., in suction rolls or blow rolls. Suction rolls generally include stationary internal suction boxes, which form zones with at least two pressure levels. In this manner, the sealing of the pressure zones occurs through sealing ledges, which generally extend at least substantially over the entire roller length.
To obtain the desired sealing action, it has generally been customary to press the sealing elements or sealing ledges against the relevant moving surface, e.g., the inner jacket surface of a perforated suction roll, via pressure elements. However, the friction appearing between the sealing element and relevant moving surface results in significant wear of the sealing element. To limit this wear, lubricants are generally applied to the sealing element via spray tubes, which increases costs. Moreover, during operation, those ledge-type sealing elements are also pressed by the respective vacuum against the inner jacket surface. Because of the sudden ventilation of the jacket perforations following the sealing ledge adjoining a respective vacuum zone, loud noise is also generated.
U.S. Pat. No. 5,580,424 discloses a sealing ledge type sealing device of the type discussed above in which the sealing ledge is radially pressed against a suction roll jacket by at least one air tube. After the sealing ledge has been applied against the suction roll jacket, the resultant ledge position is fixed by laterally pressing the sealing ledge against a bearing block, whereupon the radial contact force is reduced to zero. However, the design of this device also includes the disadvantage that, due to the frictional fixing, a respectively desired positioning of the sealing ledge cannot be maintained with the necessary accuracy. Instead, there is a danger that the positioning of the sealing ledge may change due to vibrations resulting in a gap of undefined width consequently developing between the sealing ledge and the vacuum roll jacket. This gap formation could lead to relatively high air leakage between the pressure chambers.